Gas turbine engine fuel injection systems generally include fuel manifolds which interconnect a plurality of fuel injecting nozzles. Typically, a plurality of fuel nozzles are circumferentially distributed about the annular fuel manifold and form a nozzle array in the combustor for injecting fuel into the combustion chamber thereof. The fuel nozzles typically comprise injector tip assemblies which constitute either a pressure atomizing nozzle or an airblast nozzle. Pressure atomizing (or air assist) nozzles inject only fuel through the core of the nozzle and use air flow about the central core to direct and atomize the fuel spray. Pure airblast nozzles provide a core airflow about which the fuel is delivered, such that energy from the core air, rather than hydraulic pressure, is used to help develop the fuel spray. Generally, airblast nozzles have less propensity for contamination and carbon deposit build-up, as the fuel passages in the nozzles tips are larger and the core air flow reduces the likelihood of carbon in the injected fuel recirculation zone condensing and accumulating on the nozzle tip surfaces.
Therefore, airblast nozzles with an air core have improved longevity, require less maintenance and are typically less expensive to manufacture than their pressure atomizing nozzle counterparts. However, incorporating such airblast nozzles with an internal fuel manifold, such as the type described in Applicant's published U.S. application US2004/0040306, may result in undue heating of the interior of the fuel manifold as a result of the flow of core air though the body of the manifold defining the main fuel passage therein. Keeping the interior of the fuel manifold near fuel temperature is important to prevent contamination in fuel passages from coking.
Therefore, there is a need for an improved fuel injection system.